1. Field of the Invention
The present invention pertains to a leaf spring arrangement, especially for attaching the pressure plate of a pressure plate assembly to a housing, comprising a plurality of adjacent leaf spring elements, where each leaf spring element has a first attachment area for establishing a connection to a first element, preferably the pressure plate, a second attachment area for establishing a connection to a second element, preferably the housing, and a connecting area extending between the first attachment area and the second attachment area.
2. Description of the Related Art
A pressure plate assembly in which a plurality of leaf spring arrangements is used is known from DE 198 48 582 and illustrated schematically in FIG. 1. This pressure plate assembly 10 comprises a housing arrangement 12, which can be fixed to a flywheel arrangement in a manner known in and of itself to form a friction clutch. A pressure plate 14 is mounted in the housing arrangement 12. The housing arrangement 12 and the pressure plate 14 are connected to each other by a plurality of leaf spring arrangements 16 arranged in a row around the circumference in such a way that the pressure plate 14 is able to move with respect to the housing arrangement 12, namely, in the same direction as that in which a rotational axis A extends, to enable the clutch to engage and disengage, but is completely unable to rotate around the rotational axis A relative to the housing 12 or is at most able to rotate within only a relatively small angular range. Both the housing 12 and the pressure plate 14 have sections 18, 20, to which the leaf spring arrangements 16 can be attached; in the case of the pressure plate 14, for example, these sections can be formed by radially outward-projecting attachment arms. In the case of the housing 12, they can take the form of several recessed areas, created during the process by which the housing was shaped.
It is known that leaf spring arrangements comprising a plurality of adjacent leaf spring elements 22, similar to those shown in FIG. 2 by way of example, can be used. These leaf spring elements 22 have a first attachment area 24 and a second attachment area 26. A hole 28, 30, through which a fastening bolt can be inserted, is provided in each of the attachment areas 24, 26. These fastening bolts then establish the connection to the associated attachment sections 18, 20.
A connecting area 32 extends between the two attachment areas 24, 26. It can be seen in FIG. 2 that the two attachment areas 24, 26 extend at an angle with respect to the connecting area 32. The attachment areas 24, 26 are essentially parallel to each other and thus bent away from the connecting area 32 in opposite directions. It can also be seen in FIG. 2 that the two attachment areas 24, 26 have the same length, starting from the point where they join with the connecting area 32. When a leaf spring arrangement or a leaf spring package consisting of a plurality of these types of leaf spring elements 22, as shown in FIG. 2, is assembled, the problem arises that, because the first and second attachment areas 24, 26 are all of the same length, the holes 28, 30 in the adjacent attachment areas 24, 26 are slightly offset from each other when these leaf spring elements 22 are laid directly on top of one another, which makes it difficult to insert the fastening bolt all the way through these holes 28, 30. After the fastening bolts have been inserted through these holes 28, 30, furthermore, the leaf spring elements are held under tension even when no outside load is being exerted on them. This tension increases significantly under load, because the leaf spring elements then have the tendency to come into even closer contact with each other; that is, they are pressed with greater force against each other. Thus more intense frictional interactions occur in the surface areas which are in contact with each other, which brings with it the danger that at least some of the leaf spring elements of a stack of this type will experience premature fatigue or breakage.
The problem just described occurs primarily in the types of pressure plate assemblies in which a self-reinforcing contact interaction occurs between the pressure plate and the friction surfaces of the clutch disk. This self-reinforcing effect can be achieved, for example, by increasing the angle by which the attachment areas 24, 26 shown in FIG. 2 are bent with respect to the connecting area 32. In the extreme case, this angle can reach a value in the range of 45xc2x0.
It is the object of the present invention to provide a leaf spring arrangement which, while providing the necessary elasticity or spring action, is easier to install and offers a prolonged service life.
In accordance with a first aspect of the present invention, this object is achieved by a leaf spring arrangement, especially for attaching the pressure plate of a pressure plate assembly to a housing, comprising a plurality of adjacent leaf spring elements, where each leaf spring element has a first attachment area for establishing a connection to a first element, preferably the pressure plate, a second attachment area for establishing the connection to a second element, preferably the housing, and a connecting area extending between the first attachment area and the second attachment area. It is also provided that at least certain areas of the minimum of two leaf spring elements between the first attachment area and the second attachment area are spaced apart.
By providing at least two leaf spring elements with at least certain areas where they do not rest against each other, free space or escape room is created, into which the various leaf spring elements can move without coming into contact with each other or pressing against each other with considerable force when they are deformed. The stress effects described above can therefore be avoided both in the presence and in the absence of load.
An especially advantageous embodiment provides that the minimum of two leaf spring elements contact each other only in the areas of their first and second attachment areas.
Preventing the two leaf spring elements from contacting each other at least along a portion of their length can be achieved, for example, by bending the first attachment area and/or the second attachment area of the minimum of two leaf spring elements at an angle to the connecting area between them, by making the first attachment area of one of the minimum of two leaf spring elements longer than the first attachment area of the other of the minimum of two leaf spring elements, and/or by making the second attachment area of one of the minimum of two leaf spring elements shorter than the second attachment area of the other of the minimum of two leaf spring elements.
Especially when a relatively large number of leaf spring elements is to be provided, it is advantageous for at least one additional leaf spring element to be installed between the minimum of two leaf spring elements and for the first attachment area and the second attachment area of the minimum of one additional leaf spring element to be essentially of equal length. At least certain areas of this minimum of one additional leaf spring element are then a certain distance away from the adjacent leaf spring element.
According to another advantageous aspect of the present invention, it can be provided that the minimum of two leaf spring elements are essentially of the same design, where the first attachment area of the first of the minimum of two leaf spring elements is essentially equal in length to the second attachment area of the other of the minimum of two leaf spring elements, and where the second attachment area of the first of the minimum of two leaf spring elements is equal in length to the first attachment area of the other of the minimum of two leaf spring elements.
In an alternative design of the present invention, which can be combined with the variant previously described, the separation of at least certain areas of the leaf spring elements from each other can be achieved by bending the first attachment areas and/or the second attachment areas of the minimum of two leaf spring elements at an angle to the areas connecting them and by providing a spacer between the two corresponding attachment areas of the minimum of two leaf spring elements extending at an angle with respect to their associated connecting areas.
Thus it is possible for the first spacer to be designed as a part separate from the minimum of two leaf spring elements, preferably being formed by the first element or by the second element e.g., by the pressure plate or the housing. As an alternative, it can be provided that the first spacer is formed as an integral part of one of the minimum of two leaf spring elements.
To provide relief also in those areas in which the leaf spring arrangements border on the first element or on the second element, it is also proposed that a second spacer be provided between the leaf spring element bordering on the first element and the first element and/or between the leaf spring element bordering on the second element and the second element.
It can also be provided that the second spacer is designed as an integral part of the leaf spring element resting against it. As an alternative, it can be provided that the second spacer is designed as a part separate from the leaf spring element resting against it.
The assembly of a leaf spring arrangement of this type can be facilitated by providing the first spacer and the second spacer on a single spacer component.
According to an alternative embodiment of the present invention, the object cited above is achieved by a leaf spring arrangement, especially for connecting the pressure plate of a pressure plate assembly to a housing, comprising a plurality of adjacent leaf spring elements, where each leaf spring element has a first attachment area for establishing the connection to a first element, preferably the pressure plate, a second attachment area for establishing the connection to a second element, preferably the housing, and a connecting area extending between the first attachment area and the second attachment area. The first attachment areas of the leaf spring elements and/or the second attachment areas of the leaf spring elements extend at an angle to their associated connecting areas, and each of the leaf spring elements has a hole in at least one attachment area, i.e., in the first or second attachment area, for a fastening bolt, which serves to attach the leaf spring elements to the first element or to the second element.
It is then also provided in accordance with the invention that, for at least one of the leaf spring elements, the hole in at least one of the attachment areas extending at an angle to the connecting area is larger in the longitudinal direction of the leaf spring element, which is essentially the same as the direction in which the leaf spring element extends between the first and the second attachment areas, than the corresponding section of the fastening bolt after insertion into its assigned hole.
In this design variant, the minimum of one leaf spring element is allowed a certain play with respect to the fastening bolt during the assembly process. This minimum of one leaf spring element can therefore be installed in a state in which no load is being exerted between it and any of the other leaf spring elements, a state which allows the fastening bolt to be inserted easily. In this way it is possible to arrive at an assembly situation in which, although the individual leaf spring elements are very close together and possibly even touching each other, their mutual contact is free of tension or compression in the load-free state of the leaf-spring arrangement.
To reduce the number of different parts, it is also proposed that at least two, preferably all, of the leaf spring elements be of the same design.
The present invention also pertains to a pressure plate assembly, comprising a housing and a pressure plate, which is connected by means of at least one leaf spring arrangement according to the invention to the housing with the freedom to move in the same direction as that in which the axis of the pressure plate assembly extends.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.